The present invention relates to an optical disk reproducing apparatus which reproduces data from an optical disk.
JP-A-2004-213863, when data is recorded on an optical disk by a run length limited (RLL) coding (1, 10), employs such a modulation scheme that “a minimum run length constraint is 1 and a maximum run length constraint is 10, and a frequency of repetition of the run length 1 in a channel bit string is limited to 5 or less” as described in Paragraph 0016, and attains an advantage that “the minimum run length constraint is 1 and the maximum run length constraint is 10, such a pattern that the run length 1 successively appears 6 times or more will not be present, and a channel bit string suitable for high density recording can be obtained” as described in Paragraph 0038.
JP-A-05-101402 discloses “such an optical disk identifying device that discriminates among the types of a plurality of optical disks by detecting light reflected from the optical disks and that comprises a first detection means for monitoring a quantity of laser light applied onto an optical disk 21 or 22 from a laser light source 60, a second detection means 72 for detecting a quantity of light applied onto the optical disk 21 or 22 and reflected thereby, and a calculation means 45 for finding a ratio between voltages detected by the first and second detection means 68 and 72; and that functions to discriminate among the optical disks by comparing the detection voltage ratio obtained by the calculation means 45 with previously-found voltage ratios in reflectivity between the plurality of types of different optical disks such as optical disks 21 and 22” as described in Paragraph 0011. And the optical disk identifying device can obtain an advantage that “the device can avoid the influences of the reflectivity caused by fluctuations of quantities of light emitted from the laser light source and can accurately discriminate among different disks, because the device is arranged to discriminate among the plurality of different optical disks by measuring a quantity of light emitted from the laser source and a quantity of light applied onto the optical disk 21 or 22 and reflected thereby, finding a ratio of the both light quantities converted to voltages, and comparing the found ratio with a reference value of the reflectivity determined by the plurality of different optical disks” as described in Paragraph 0012.
The optical disk identifying device disclosed in JP-A-05-101402 “discriminates among the plurality of different optical disks by measuring the quantity of light emitted from the laser source and the quantity of light applied onto the optical disk 21 or 22 and returned therefrom, finding the ratio of the both light quantities converted to voltages, and comparing the found ratio with the reference value of the reflectivity determined by the plurality of different optical disks”. For this reason, the device can discriminate among different optical disks having different physical characteristics, but cannot discriminate among different types of optical disks having a common physical characteristic and thus cannot cope with reproduction control suitable for each of the optical disks, because the quantities of light returned therefrom become the same.